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DECODE WAYS - LEETCODE PROBLEM 91

A message containing letters fromA-Zis being encoded to numbers using the following mapping:'A' -> 1 'B' -> 2 ... 'Z' -> 26 Given a non-empty string containing only digits, determine the total number of ways to decode it.Example 1:Input: "12" Output: 2 Explanation: It could be decoded as "AB" (1 2) or "L" (12). Example 2:Input: "226" Output: 3 Explanation: It could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).class Solution { public int numDecodings(String s) { int ways=0; ways=countDecoding(s.toCharArray(),s.length()); return ways; } int countDecoding(char[] digits, int n){ // System.out.println(" digits "+disgits[0]); // for base condition "01123" should return 0 // base cases if (n == 0 || (n == 1 && digits[0]!='0')) ret…

EDIT DISTANCE PROBLEM - LEETCODE 72

Given two words word1 and word2, find the minimum number of operations required to convert word1 to word2.You have the following 3 operations permitted on a word:Insert a characterDelete a characterReplace a characterExample 1:Input: word1 = "horse", word2 = "ros" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e')Solution:- class Solution { public int minDistance(String word1, String word2) { if(word1.length()==0){ return word2.length(); } if(word2.length()==0){ return word1.length(); } if(word1.length()==0 && word2.length()==0){ return 0; } int[][] result=new int[word1.length()+1][word2.length()+1]; for(int i=0;i<=word1.length();i++){ result[i][0]=i; } for(int j=0;j<=…

TWO SUM -LEET CODE PROBLEM 1

https://leetcode.com/problems/two-sum/Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.You may assume that each input would have exactly one solution, and you may not use the same element twice.You can return the answer in any order.Example 1:Input: nums = [2,7,11,15], target = 9 Output: [0,1] Output: Because nums[0] + nums[1] == 9, we return [0, 1]. Example 2:Input: nums = [3,2,4], target = 6 Output: [1,2] Example 3:Input: nums = [3,3], target = 6 Output: [0,1]class Solution {    public int[] twoSum(int[] nums, int target) {        HashMap<Integer,Integer> map=new HashMap<Integer,Integer>();        for(int i=0;i<nums.length;i++){            if(map.get(nums[i])==null){                map.put(target-nums[i],i);            }            else{                return new int[]{map.get(nums[i]),i};            }        }        return null;    }}

Calculating size of User and Cache storage

user storage:-
it can be solved using same scenario as mentioned in first article .

https://tech.nazarmubeenworks.com/2019/08/basics-of-system-design-chapter-0.html


Suppose there are 12 Million of users are adding every year meaning 1 Million per month.
So if we consider 5 year there will be around 60 million of users. Now in terms of data we can look to our DB table and get information about it. A user will be generally having name , id , address , some forien keys .
Lets assume 10 columns with each column on an average storing 4 byte of data.
10*4 = 40 bytes of data for one user.
60 * 10^6 * 40 = 2400 * 10^6 = 2.4 * 10^9 = 2.4 GB of data we need to store only user values.
Also while calculating storage for the user there is also one important point we need to remember is of ids. If we are going to have 60 Million of users which means 60*10^6 users so unique id’s will be
as we know below figures are almost equal
2^10=10^3 then 60*(10^3)^2 = 2^20 *2^6
which means we almost need 26 …

Basics of System Design

This article is first one from the series of articles dedicated to system design interviews. Here i am going to present the base scenario to consider before starting to solve system design problems.
Questions to ask?
1) what is the number of requests a website will recieve in a day/month/second? 2) what is the amount of memory a website will deal in a day/month/second? 3) what is the number of servers that can accomodate these requests?
To answer this , first we need to remember the below numbers:-
1 million = 10 lakh = 1000000 = 10^6 1 billion = 1000 million = 10^9
1 KB = 1024 B = 10^31 MB= 10^6 = 1024 KB 1 GB= 10^9 = 1024 MB1 TB = 10^12 = 1024 GB
Memory we need to see in BytesRequests we need to see in numbers
example :-
suppose a website recieves 100M requests every month then:-
requests per day = request per month /24 = 416700 requests requests per second = requests per day / (24*3600) = 4.8 requests per second
memory:-
if we take 20:80 principal where 20 percent is write and 80 percent is …

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